(1) Field of the Invention
This invention relates to an assistor for operating the transmission of an automotive vehicle, and more specifically to such an assistor which is installed between the gearshift lever and the transmission in such a way that a directional control valve is actuated by the operation of the gearshift lever to supply a fluid to a cylinder and thereby actuate a piston and use the force of its motion as the output with which to move the shift lever and the associated shift jaw of the transmission.
(2) Description of the Prior Art
The development of extensive expressway systems in recent years has led to the introduction of bigger and bigger motor vehicles, naturally with engines of greater capacities and higher outputs than before. Consequently, larger transmissions have been adopted and, to lessen the efforts required by the drivers in operating such transmissions, varied attempts have been made including the provision of some power assistance system, or assistor, between the gearshift lever and the transmission.
Those systems for operating the transmissions of the cab-overs that constitute a large percentage of big trucks have limitations in space, especially in height, for installation. To solve the problem, it is customary that, as typically shown in FIG. 1, the linkage of the gearshift lever is terminated on one side of the transmission so that the operating force applied to the lever opens a valve of the assistor arranged in parallel with the transmission. The force multiplied thereby is taken out as the output to rotate a shift rod extending over and across the transmission and cause a shift lever attached to the rod to actuate the shift jaws of the transmission.
The conventional mechanism for operating the transmission will be described in detail below with reference to FIGS. 1 to 3. FIG. 1 shows an arrangement of the components of the mechanism. The numeral 1 indicates the casing that contains the shift rod and the shift lever and is mounted crosswise on the transmission 2. The casing 3 of the assistor is located on one end of the casing 1, in parallel with the transmission 2. A lever 4 of the assistor, provided on one side of the casing 3, is connected with the gearshift lever 5 below the driver's seat by linkage. In FIG. 1, 6 is a selector lever, and 7 is the clutch.
FIG. 2 is a sectional view, on an enlarged scale, taken on the line A--A of FIG. 1. The above-mentioned lever 4 (hereinafter referred to as the first shifter lever) is integrally coupled to a second shifter lever 9 engaged on the input side of the assistor 8 and is made turnable with respect to the casing 3.
The shift rod 10 is rotatsbly held by the casing 1, with one end extended into the casing 2. Onto this end portion is fixedly mounted a third shifter lever 11 engaged on the output side of the assistor. The shift rod 10 has splines 12 formed on an intermediate portion on which a shift lever or actuator 13 is fitted. In FIG. 2, 14 is a select lever integrally joined to the selector lever 6 of FIG. 1, and 15 is a shift jaw assembly of the transmission 2, comprising three shift jaws or elements 15.sub.1, 15.sub.2, 15.sub.3 meshed with the respective gears of the transmission (not shown).
FIG. 3, a sectional view taken on the line B--B of FIG. 2, illustrates the construction of the assistor 8. The assistor includes a cylinder 16 formed in its casing 3. A hollow piston rod 17 is slidably housed in the cylinder 16, and its piston 18 divides the space in the cylinder 16 into two pressure chambers 19, 20.
An actuating rod 21 is slidably fitted in the bore of the piston rod 17. The actuating rod 21 holds a length of pipe 22 on its end. The pipe 22 has an axial passage 23 for compressed air and also ports 24 to communicate one end of the passage with the bore of the piston rod 17.
In the bore of the piston rod 17, there are a pair of floating valves 25 and 26 held apart, on both sides of the ports 24, stationary valve seats 27, 28 located on the outer sides of the valves and fixedly mounted on the piston rod 17, and valve lifters 29, 30 located on the farther outer sides of the valve seats to actuate the floating valves 25, 26.
The floating valves 25, 26 are biased away from each other and kept in contact with the stationary valve seats 27, 28 by a spring 31 disposed in between. Additional springs 32, 33 are interposed between the valve seats 27, 28 and valve lifters 29, 30 to bias the valve lifters outwardly from each other so that their outer ends are abutted, respectively, against a flange 34 of the pipe 22 and an end 35 of the actuating rod 21.
In the same figure: 36 is a port for supplying compressed air; 37 is a chamber formed by the floating valve seats 25, 26 in the bore of the piston rod 17; 38, 39 are air passages establishing communication between the bore of the piston rod 17 and the chambers 19, 20 of the cylinder 16; 40, 41 are exhaust passages formed between the pipe 22 and the valve lifters 29, 30; 42 is an exhaust passage formed in the piston rod 17; 43, 44 are exhaust passages formed in the actuating rod 21; 45 is an exhaust hole formed in a cover 46; and 47 is a detent mechanism keeping the piston rod 17 and the actuating rod 21 engaged.
The detent mechanism 47 is of the construction now to be described. It includes a hollow arm 48 fixedly secured to the piston rod 17, with a large-diameter chamber 49 formed in the bore of the arm 48. A ball 50 is loosely fitted in the chamber and biased by a spring 51 toward the control rod 21. On the other hand, the actuating rod 21 is provided with protrusions 52, 53 perpendicular to its axis on the opposite sides, and the protrusion 52 has an annular recess 54 at the outer end, so that the ball 50 fits in the recess 54 to keep the piston rod 17 and the actuating rod 21 engaged.
The assistor 8 built in this manner holds the protrusion 53 of the actuating rod 21 engaged with the second shifter lever 9, and holds the arm 48 of the piston rod 17 engaged with the third shifter lever 11.
The conventional mechanism for operating the transmission as so far described operates in the following way. As the gearshift lever 5 shown in FIG. 1 is manipulated for selection, the force is transmitted so as to turn the selector lever 6 and therefore move the select lever 14 in FIG. 2 that is directly connected to the lever 6 leftwardly or rightwardly as viewed in the same figure. Accordingly, the shift lever 13 is moved leftwardly or rightwardly along the splines 12 until it engages the shift jaw 15.sub.1, 15.sub.2, 15.sub.3 of the transmission 2. Next, the gearshift lever 5 is moved for shifting, and the force is transmitted so as to turn the first shifter lever 4 and the second shifter lever 9 directly connnected to the lever 4, thereby moving the actuating rod 21, through the protrusion 53, leftwardly or rightwardly as viewed in FIG. 3.
If, for example, the actuating rod 21 is forced rightwardly, the pipe 22 secured to the rod moves to the right, too, with its flange 34 pushing the valve lifter 29 rightwardly. The rightward movement of the valve lifter 29 urges the floating valve 25 rightwardly away from the stationary valve seat 27. The compressed air that has reached the chamber 37 via the supply port 36, passage 23, and port 24, then flows through the space between the floating valve 25 and the stationary valve seat 27 and further through the air passage 38 into the pressure chamber 19 of the cylinder 16, where it forces the piston 18 rightwardly. Inasmuch as the piston 18 is formed in one piece with the piston rod 17, the piston rod moves rightwardly together with the piston, also carrying the arm 48 secured to the rod rightwardly. This rightward movement of the arm is transmitted to the second shifter lever 11, thus causing the shift rod 10 shown in FIG. 2 to rotate. The rotation of the shift rod is accompanied with turning of the shift lever 13 for frontward or rearward movement (as viewed in FIG. 2) of the shift jaw 15.
With the mechanism for operating the transmission, as will be obvious from the foregoing, the force with which the gearshift lever 5 is operated need not be great but just enough to open the valve. The open valve permits compressed air to act on the piston 18 for the multiplication of force, and the resulting output in turn causes the shift rod 10 to rotate and thereby actuate the shift jaw 15 through the shift lever 13.
Following the conclusion of the shifting procedure for the assistor 8, release of the operating force off the gearshift lever brings the piston rod 17 and the actuating rod 21 to points slightly to the right of the casing 3 as viewed in FIG. 3, but the piston rod 17 and the actuating rod 21 resume their relative position shown in FIG. 3. This allows compressed air to leave the cylinder 19 by way of the air passages 38 and outlet passages 40, 42 to the outside.
As described above, the conventional mechanism for operating the transmission converts the turning motion of the first shifter lever 4 first into a straight line motion by means of the assistor 8 and then reconverts the multiplied output of the straight line motion into a rotational motion of the shift rod 10. Such an operating mechanism produces loss of motion in transmission. Moreover, the ordinary assistor 8 is rather complex in construction and large in size.